The present invention relates to a scroll compressor having spiral type scroll wraps, and more particularly, to a double toothed type oil-free scroll compressor suitable for use in air compressors.
Conventionally, scroll compressor have been used for refrigeration and air conditioning, which comprise a stationary scroll having a spiral wrap provided upright on an end plate and an orbiting scroll having a wrap adapted to engage with the wrap of the stationary scroll. In recent years, such scroll compressors have also been used as an air compressor because of their advantageous low noise.
Incidentally, convenience in use has increased a demand for scroll compressors for air compression, which range from a low air volume type for painting or the like to a high air volume type for a factory air source or the like. In order to meet a demand for high air volumes, a so-called double toothed type scroll compressor having an orbiting scroll with wraps on both sides of an end plate has gotten in the spotlight. An example of such double toothed type scroll compressor is described in Japanese Patent Laid-Open Nos. 10-246189 and 10-252668.
A scroll compressor, being one type of displacement type compressors, must be formed with an enclosed space. In particular, in the case of an oil-free compressor, any seal based on an oil film is not provided, and so an elastic member called a tip seal is disposed as a seal member between a tip end of a scroll wrap and an end plate, which the scroll wrap faces. It is required that such tip seal be excellent in sealing quality and low in friction. Therefore, a high polymer material such as a fluorine contained resin is often used for the tip seal.
It has proved from experimental studies conducted by the inventors of the present application that the use of a resin material for the tip seal may possibly cause the following disadvantage. That is, scroll compressors, in particular, oil-free scroll compressors for air compression, use grease-filled bearings for supporting a crankshaft. In operation, oil films of the bearing make electrical insulation between the crankshaft and a stationary scroll and between the crankshaft and an orbiting scroll. Both orbiting and stationary scroll members are formed by coating an aluminum alloy stock with an alumite film, which is an insulator to make electrical insulation between the orbiting scroll and the stationary scroll.
In ordinary use, the compressor is used in a state in which the stationary scroll is grounded. Meanwhile, the orbiting scroll and the crankshaft are not grounded. When the compressor is started in this state, static electricity is produced by sliding of the tip seal on the end plate surface of the scroll member or by sliding of a belt on pulleys, and has its electric charge accumulated in the crankshaft and orbiting scroll. While an accumulating amount of electric charge is not so much for a low capacity compressor, it increases remarkably with an increase in compressor capacity. Such electric charge generates an electric potential difference between inner and outer races of a roll bearing, and thus hydrogen ions induced accumulate in a location of high stresses within the bearing. The accumulated hydrogen ions change the internal structure of a bearing steel to create crack inside of the bearing steel. In the worst case, the roll bearing may be damaged electrically.
The present invention has been devised to solve the above-mentioned disadvantages involved in the prior art, and has its object to operate a scroll compressor over a long term with high reliability.
To attain the above object, a scroll compressor according to the present invention comprises an orbiting scroll having a spiral wrap; a stationary scroll having a spiral wrap adapted to engage with the wrap of said orbiting scroll; a crankshaft for driving said orbiting scroll; and a tip seal mounted on a tip end of the wrap of at least one of said stationary scroll and said orbiting scroll, and wherein at least one of said orbiting scroll and said crankshaft is formed of an electrically conductive material, and further comprises a conducting means for providing electrical conduction of said orbiting scroll to said stationary scroll in operation of said scroll compressor.
To attain the above object, another scroll compressor according to the present invention comprises an orbiting scroll having a spiral wrap; a stationary scroll having a spiral wrap adapted to engage with the wrap of said orbiting scroll; a crankshaft for driving said orbiting scroll; and a tip seal mounted on a tip end of the wrap of at least one of said stationary scroll and said orbiting scroll, and wherein at least one of said orbiting scroll and said crankshaft is subjected to insulator or nonconductor coating surface treatment, and further comprises a conducting means for providing electrical conduction of said orbiting scroll to said stationary scroll in operation of said scroll compressor.
In any one of the above-described scroll compressors, a slip ring or a brush may be provided on an end of said crankshaft to conduct static electricity accumulated in said crankshaft to the outside of said crankshaft; and said tip seal may be formed of an electrically conductive material, and a surface of said orbiting scroll or said stationary scroll, with which said tip seal contacts, may be made electrically conductive. Further, it is desired that an annular dust wrap is provided on a side diametrically outside of the wrap of said stationary scroll, and a conductive dust seal is disposed on a tip end of said dust wrap.
Further, in any one of the above-described scroll compressors, a roll bearing may be provided for supporting the crankshaft, of which inner and outer races are electrically connected to each other in operation; the roll bearing may contain an electrically conductive grease; a roll bearing may be provided for supporting the crankshaft, and wherein at least one of inner and outer races, and rolling elements of the roll bearing may be formed of an electrical insulator; and a roll bearing may be provided for supporting the crankshaft, and at least one of inner and outer races, and rolling elements of the roll bearing may be formed of a material, which forms a nonconductor film. In addition, the material forming a nonconductor film may be a martensitic stainless steel.
To attain the above object, any one of the above-described scroll compressors may be an oil-free compressor, the orbiting scroll may have spiral wraps on both sides of an end plate, the stationary scroll may comprise a pair of stationary scroll members each having a wrap adapted to engage with each of the wraps of the orbiting scroll, and working chambers defined by the wraps of the orbiting scroll and the stationary scroll may be free of entry of an oil such as lubricant or the like.
To attain the above object, a still another scroll compressor according to the present invention comprises an orbiting scroll having a wrap; a stationary scroll having a wrap adapted to engage with the wrap of the orbiting scroll; a crankshaft and an auxiliary crankshaft disposed on a side diametrically outside of the wraps of both the orbiting scroll and the stationary scroll and for driving the orbiting scroll; a first pulley mounted on the crankshaft and a second pulley mounted on the auxiliary crankshaft; and a belt trained around outer peripheral sides of the first and second pulleys; and the belt is electrically connected to the first and second pulleys.
To attain the above object, a still further scroll compressor according to the present invention comprises an orbiting scroll having a wrap; a stationary scroll having a wrap adapted to engage with the wrap of the orbiting scroll; a crankshaft and an auxiliary crankshaft for driving the orbiting scroll and disposed on a side diametrically outside of the wraps of both the orbiting scroll and the stationary scroll; a first pulley mounted on the crankshaft and a second pulley mounted on the auxiliary crankshaft; and a belt trained around outer peripheral sides of the first and second pulleys; and electrical insulation is made between the crankshaft and the first pulley and between the auxiliary crankshaft and the second pulley.
To attain the above object, a further scroll compressor according to the present invention comprises an orbiting scroll having spiral wraps on both sides of an end plate; a pair of stationary scrolls having wraps adapted to engage with the wraps of the orbiting scroll; a main crankshaft and an auxiliary crankshaft for rotationally driving the orbiting scroll, and disposed on a side diametrically outside of the wraps of both the orbiting scroll and the stationary scrolls; a plurality of roll bearings for supporting the main crankshaft and the auxiliary crankshaft; first and second pulleys mounted on the main crankshaft and auxiliary crankshaft, respectively; a resin belt trained around the first and second pulleys; resin tip seals held in grooves formed on tip ends of the orbiting scroll wraps and the stationary scroll wraps; and static electricity discharging means provided to discharge static electricity, which is produced in the timing belt portion and the tip seal portions, from the orbiting scroll to the stationary scrolls.
In the above-described scroll compressor, the static electricity discharge means may be a slip ring provided on an end of at least one of the main crankshaft and the auxiliary crankshaft; and the static electricity discharge means may comprise an electrically conductive grease for preventing the accumulation of static electricity in the roll bearings. Also, it is desired that the bearings comprise grease-lubricated bearings, and a base oil of the grease is an ether-based synthetic oil and a thicker therefor is a urea compound.
That is, in an oil-free scroll compressor, at least one of the orbiting scroll and the crankshaft may be brought into contact with the stationary scroll or other grounding members via an electrically conductive member to maintain the orbiting scroll, crankshaft, and the stationary scroll in the same electric potential; or electrical damages on the bearings may be prevented by arranging an insulator or the like even when electric potential difference is present between the orbiting scroll, stationary scroll, and the crankshaft.